swap versus swapAt

The swap(_:_: ) method in Swift 3 works on "pass by reference principle" and swaps two elements of a given array on the spot. In pass by reference, actual memory addresses are used rather than values:

var integerArray = [1, 2, 4, 3, 5]
swap(integerArray [2], integerArray [3])

As you can see, the parameters are passed as in out parameters, which means the actual references or placeholder addresses are accessible directly inside the function. On the other hand, Swift 4’s swapAt(_:_:) works on “pass by value” principle and only the corresponding indices are passed to the function to be swapped:

integerArray.swapAt(2, 3)

The swap(_:_:) function will not be seen in Swift 4, because it will be deprecated and removed, and you have a couple of approaches to replace it. The first approach uses a temporary constant as follows:

let temp = a
a = b
b = temp

The second takes advantage of Swift's built in tuples, as follows:

(b, a) = (a, b)